1. Field of the Invention
The present invention relates to a ring network supervisory system supervising the communication status of a ring network in which a plurality of nodes are interconnected in a ring so that data may be exchanged with each other via a ring-form transmission line, and more particularly to a simply-structured ring network supervisory system capable of detecting an abnormal frame which cannot be transmitted and of immediately recovering the detected abnormal frame.
2. Description of the Related Art
Conventionally, a ring network in which a plurality of nodes are interconnected in a ring so that data may be exchanged with each other via a ring-form transmission line is known. Also known is a ring network supervisory system, such as the one disclosed in Japanese Patent Laid-Open Application No. Hei 3-145239, which has a counter field in a token frame so that the values may be added.
The token ring supervisory method disclosed in the above patent publication provides, in a token frame which circulates around the ring, the counter field which is used for adding values. Each node comprises receiving means for receiving a frame from the predecessor on the transmission line, transmitting means for transmitting a frame to the successor on the transmission line, counter holding means for holding the value of the counter field in a token frame passing through the node, and frame processing means having a received-frame processing function processing the received frame.
According to this token ring supervisory system, each time a node receives a token ring, the node stores, and then adds xe2x80x9c1xe2x80x9d to, the value of the counter field of the received frame. In addition, when the node receives a token frame, it calculates the difference between the previously-stored counter field value and the current counter field and checks if the calculated difference is equal to the total number of nodes in the token ring. If the communication functions of all nodes in the ring are normal, the calculated difference should be equal to the total number of nodes; if the communication function of a node in the token ring is abnormal, the calculated difference should not be equal to the total number of nodes.
Therefore, whether or not the communication functions of all nodes in the token ring are normal may be diagnosed by checking if the calculated difference is equal to the total number of nodes. If, as a result of this diagnosis, the communication function of a node in the token ring is found abnormal, the failed node with the abnormal communication function is isolated by sequentially comparing the stored values of each two neighboring nodes.
However, if the conventional token ring supervisory method described above is used in a ring network composed of a plurality of nodes, among which data may be exchanged with each other, connected by a ring-form transmission line which allows a communication frame to be circulated in one direction and, in addition, a plurality of communication frames to be transmitted at the same time, each node requires a plurality of memories, each for storing the value of a counter corresponding to each of a plurality of communication frames, as well as a plurality of frame control circuits. This increases and the size of, and complicates the configuration of, the supervisory circuit installed in each node.
Thus, there has been a long felt need, among those skilled in the art, for the development of a new technology of building a simply-structured system, capable of detecting and then immediately recovering an abnormal frame which cannot be transmitted normally even in a ring network described above.
In view of the foregoing, it is an object of the present invention to provide a simply-structured ring network supervisory system capable of detecting and then immediately recovering an abnormal frame which cannot be transmitted normally, even when the system is used in a ring network composed of a plurality of nodes, among which data may be exchanged with each other, connected via a ring-form transmission line which allows a communication frame to be circulated in one direction and, in addition, a plurality of communication frames to be transmitted at the same time.
To achieve the above object, there is provided a ring network supervisory system supervising a communication status of a ring network to which a plurality of nodes are connected via a ring-form transmission line for exchanging data, the transmission line allowing a communication frame to be circulated in one direction and, in addition, a plurality of communication frames to be on the transmission line at the same time, the communication frame comprising: a source address description area in which a source address of a source node of the communication frame is described; and a passage counter description area in which a passage counter count value representing a passage count is described, the passage count being incremented each time the communication frame passes through each of the plurality of nodes, each of the plurality of nodes comprising: frame reception means for receiving the communication frame from a neighboring node located in an upstream of the node; local node address storage means for storing a local node address assigned uniquely to the node; one-round checking information storage means for storing one-round checking information referenced to check if the communication frame has circulated around the ring network; frame checking means for referencing a description content of the communication frame received by the frame reception means to check to see if the received communication frame is an occupied frame originated from any of the plurality of nodes or a non-occupied frame not originated from any of the plurality of nodes, the plurality of nodes including the node; address comparison checking means for comparing the source address described in the received communication frame with the local node address stored in the local node address storage means when the frame checking means find that the received communication frame is the occupied frame; passage counter comparison checking means for checking a relation between the passage counter count value described in the received communication frame with the one-round checking information stored in the one-round checking storage means when the address comparison checking means find that the source address and the local node address do not match; passage counter operation means for determining the received frame is normal and for performing a predetermined operation on the passage counter count value described in the passage counter description area in the communication frame when the passage counter comparison checking means find that the relation between the passage counter count value and the one-round checking information do not satisfy a one-round checking condition; abnormal-frame reception signal transmission means for determining that the received communication frame is an abnormal frame and for transmitting an abnormal frame reception signal indicating that the abnormal frame has been received when the passage counter comparison means find that the relation between the passage counter count value and the one-round checking information satisfies the one-round checking condition; frame generation control means for generating the communication frame when the node is the source of the communication frame, the source address description area describing the local node address and the passage counter description area describing the passage counter count value to be used as an initial value, and for generating the communication frame when the node is not the source of the communication frame, the passage counter count description area describing the passage counter count value calculated by the passage counter operation means; and frame transmission means for transmitting the communication frame generated by the frame generation control means to the neighboring node located in a downstream of the node.
According to the present invention, upon receiving a communication frame, the frame checking means first references the description content of the communication frame to check if the received communication frame is an occupied frame which was issued by one of a plurality of nodes including this node or a non-occupied node which is not a frame issued from any of the plurality of nodes.
If it is found, as a result of this frame checking, that the received communication frame is an occupied frame, the address comparison checking means compares the source address described in the received communication frame with the address of the node.
If it is found, as a result of this address comparison, that the source address and the address of this node do not match, the passage counter comparison means checks the relation between the passage counter count value described in the received communication frame and the one-round checking information stored in the one-round checking information storage means.
If it is found, as a result of this passage counter checking, that the relation between the passage counter count value and the one-round checking information does not satisfy the one-round checking condition, then the passage counter operation means judges that the received communication frame is a normal communication frame and performs the predetermined operation on the passage counter count value described in the passage counter count description area of the communication frame. If it is found that the relation between the passage counter count value and the one-round checking information satisfies the one-round checking condition, then the abnormal-frame reception signal transmission means judges that the received communication frame is an abnormal communication frame and sends an abnormal frame reception signal indicating that the abnormal frame has been received.
In addition, when the node is the source of the communication frame, the frame generation control means describes the address of the node in the source address description area and generates a communication frame whose passage counter description area has been changed to the passage counter count value used as the initial value. When the node is not the source of the communication frame, the means generates a communication frame whose passage counter description area has been changed to the count value calculated through the predetermined operation.
Then, the frame transmission means transmits the generated communication frame to the node located in the downstream.
Therefore, the present invention provides a simply-structured ring network supervisory system capable of detecting and then immediately recovering an abnormal frame which cannot be transmitted normally, even when the system is used in a ring network composed of a plurality of nodes, among which data may be exchanged with each other, connected via a ring-form transmission line which allows a communication frame to be circulated in one direction and, in addition, a plurality of communication frames to be transmitted at the same time.
In a preferred embodiment of the present invention, the frame generation control means further comprises a returned-frame regeneration function which, when the address comparison checking means find that the source address and the local node address match, judges that the communication frame originated by the node has returned to the node, discards the received communication frame, and generates a new free token frame which is the non-occupied frame.
In this embodiment, when the address comparison checking means find that the source address and the local node address match as a result of the checking, the frame generation control means judges that the communication frame originated by the node has returned to the node, discards the received communication frame, and generates a new free token frame which is the non-occupied frame.
In a preferred embodiment of the present invention, the frame generation control means further comprises an abnormal frame regeneration function which, when the passage counter comparison means finds that the relation between the passage counter count value and the one-round checking information satisfies the one-round checking condition, judges that the received communication frame is the abnormal frame, discards the received communication frame, and generates a new free token frame which is the non-occupied frame.
In this embodiment, when the passage counter comparison means finds that the relation between the passage counter count value and the one-round checking information satisfies the one-round checking condition, the frame generation control means judges that the received communication frame is the abnormal frame, discards the received communication frame, and generates a new free token frame which is the non-occupied frame. Therefore, even when an abnormal condition occurred on the ring-form transmission line or in any of the nodes, an abnormal frame which is generated due to the abnormal condition and which would circulate around the ring network semi-permanently if left unattended may be returned to the normal state. As a result, a highly-reliable ring network supervisory system protected against abnormal conditions may be implemented.
In a preferred embodiment of the present invention, when the node has data waiting to be transmitted, the frame generation control means generates the communication frame containing the data waiting to be transmitted instead of the new free token frame which is the non-occupied frame.
In this embodiment, when the node has data waiting to be transmitted, the frame generation control means generates the communication frame containing the data waiting to be transmitted instead of the new free token frame which is the non-occupied frame.
This gives a node, which has received a frame generated by itself or an abnormal frame, a chance to transmit a communication frame containing data waiting to be transmitted in the node. Therefore, each node may get transmission rights more often, thereby increasing the throughput of the whole ring network system.
In a preferred embodiment of the present invention, when the frame checking means finds that the received communication frame is the non-occupied frame, the frame generation control means rewrites the passage counter count value of the received communication frame and generates a new communication frame.
In this embodiment, when it is found that the received communication frame is the non-occupied frame as a result of frame checking through the frame checking means, the frame generation control means rewrites the passage counter count value of the received communication frame and generates a new communication frame.
In a preferred embodiment of the present invention, when the passage counter checking indicates that the relation between the passage counter count value and the one-round checking information satisfies the one-round checking condition, the passage counter comparison checking means comprises an abnormal frame reception signal transmission function which judges that the received communication frame is the abnormal frame and transmits an abnormal frame reception signal indicating that the abnormal frame has been received.
In this embodiment, when the passage counter checking indicates that the relation between the passage counter count value and the one-round checking information satisfies the one-round checking condition, the passage counter comparison checking means judges that the received communication frame is the abnormal frame and transmits an abnormal frame reception signal indicating that the abnormal frame has been received.
In a preferred embodiment of the present invention, the ring network supervisory system comprises a plurality of communication supervisory means each connected to one of the plurality of nodes and supervising the communication status of the node, wherein the passage counter comparison checking means transmits the abnormal frame reception signal indicating that the abnormal frame has been received to the communication supervisory means connected to the node to inform the communication supervisory means connected to the node that the abnormal frame has been received.
In this embodiment, because the node receiving an abnormal frame immediately informs the communication supervisory means connected to the node that the abnormal frame has been received, each of the plurality of communication supervisory means can keep track of the abnormal frame generation status in the system.
In a preferred embodiment of the present invention, the predetermined operation performed by the passage counter operation means is to add xe2x80x9c1xe2x80x9d to the passage counter count value.
In this embodiment, the predetermined operation performed by the passage counter operation means is to add xe2x80x9c1xe2x80x9d to the passage counter count value.
In a preferred embodiment of the present invention, the predetermined operation performed by the passage counter operation means is to subtract xe2x80x9c1xe2x80x9d from the passage counter count value.
In this embodiment, the predetermined operation performed by the passage counter operation means is to subtract xe2x80x9c1xe2x80x9d from the passage counter count value.
To achieve the above object, there is provided a ring network supervisory system supervising a communication status of a ring network to which a plurality of nodes are connected via a ring-form transmission line for exchanging data, the communication frame comprising: a source address description area in which a source address of a source node of the communication frame is described; and a passage counter description area containing a value which is updated each time the communication frame passes through each of the plurality of nodes, each of the plurality of nodes comprising: frame reception means for receiving the communication frame; address comparison means for comparing the source address described in the received communication frame with a local node address; one-round checking means for checking if the received communication frame has circulated around the ring network, based on a counter value stored in the passage counter description area of the received communication frame, when the address comparison means judges that the source address and the local node address do not match; passage counter operation means for judging that the received communication frame is a normal frame and for performing a predetermined operation on the counter value stored in the passage counter description area in the received communication frame to update the counter value when the one-round checking means judges that the received communication frame has not yet made a one-round circulation; abnormal-frame reception signal transmission means for judging that the received communication frame is an abnormal frame and for transmitting a signal indicating that the abnormal frame has been received when the one-round checking means find that the received communication frame has made the one-round circulation; frame generation control means for generating the communication frame when the node is the source of the received communication frame, the source address description area describing the local node address and the passage counter description area describing an initial value, and for generating the communication frame when the node is not the source of the received communication frame, the passage counter description area describing the counter value updated by the passage counter operation means; and frame transmission means for transmitting the communication frame generated by the frame generation control means.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.